JP2005194167A - Chromium chloride aqueous solution and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a chromium chloride aqueous solution with an extremely less residual organic carbon content and its manufacturing method. <P>SOLUTION: The chromium chloride aqueous solution contains oxalic acid of ≤8 wt.% vs. chromium. The total organic carbon content is preferably ≤4 wt.% vs. chromium. Preferably, free chlorine ion uncombined with Cr is not substantially contained. The chromium chloride aqueous solution is manufactured by adding an organic reducing agent into a chromic acid aqueous solution as a first step of reaction to reduce a part of the chromic acid in advance and then adding a mixture of hydrochloric acid and the organic reducing agent to complete the reaction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an aqueous chromium chloride solution and a method for producing the same.

  Conventionally, chromium chloride has been manufactured by adding sulfuric acid to a sodium dichromate solution obtained by alkaline oxidation roasting of ore and reducing it with an organic substance to obtain a chromium sulfate solution. A method is known in which a precipitate of chromium oxide or chromium carbonate is formed, filtered, washed with water, and then dissolved by adding hydrochloric acid. Alternatively, high-carbon ferrochrome obtained by reducing chromium ore with an electric furnace using a carbon reducing agent is extracted with sulfuric acid, and this solution is electrolyzed to form metallic chromium, and hydrochloric acid is added to metallic chromium to form chromium chloride. Manufacturing methods are also known.

  Apart from this, the present applicant has proposed a method for producing a high-purity chromium chloride aqueous solution by reacting a chromic acid aqueous solution with hydrochloric acid and an organic reducing agent that can be decomposed into carbon dioxide and water by reacting with chromic acid. (For example, refer to Patent Document 1).

  In addition to the chromium chloride aqueous solution, a chromium nitrate aqueous solution is also known as a metal surface treatment agent. As a method for obtaining a hexavalent chromium-free chromium nitrate aqueous solution, a method in which the total amount of organic carbon in the aqueous solution is in a specific range has been proposed (see Patent Document 2).

Japanese Patent Laid-Open No. 1-176227 JP 2002-339082 A

  Among conventional methods, the method of dissolving chromium hydroxide with hydrochloric acid is very difficult to wash the chromium hydroxide precipitate obtained by adding caustic soda or soda ash to chromium sulfate, and impurities such as sodium or sulfate in chromium hydroxide Have problems that cannot be removed.

  Accordingly, an object of the present invention is to provide chromium chloride and a method for producing the same, which can eliminate the various disadvantages of the above-described prior art.

  The present invention achieves the above object by providing a chromium chloride aqueous solution characterized in that the content of oxalic acid is 8% by weight or less based on chromium.

  In the present invention, an organic reducing agent comprising a monohydric alcohol or a dihydric alcohol is added to a chromic acid aqueous solution as a first step of the reaction to reduce a part of chromic acid in advance, The present invention provides a method for producing an aqueous solution of chromium chloride characterized in that the reaction is completed by mixing and adding an organic reducing agent.

  Furthermore, the present invention provides a chromium chloride crystal having an oxalic acid content of 2% by weight or less based on chromium.

  Further, in the present invention, as a first step of the reaction, an organic reducing agent comprising a monohydric alcohol or a dihydric alcohol is added to the aqueous chromic acid solution to reduce part of the chromic acid in advance, and then hydrochloric acid and the Chromium chloride characterized in that an organic reducing agent is mixed and added to complete the reaction to obtain a chromium chloride aqueous solution, and then the chromium chloride aqueous solution is concentrated by heating and further cooled to precipitate chromium chloride crystals. A method for producing a crystal is provided.

  The chromium chloride aqueous solution and the chromium chloride crystal of the present invention have a very small amount of oxalic acid, and when this is used to perform metal surface treatment, an excellent gloss product can be obtained. Further, according to the production method of the present invention, chromium chloride having an extremely small amount of oxalic acid can be produced industrially advantageously.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The aqueous chromium chloride solution of the present invention is characterized by a low level of oxalic acid, which is a kind of organic substance. Specifically, it has been found that when the content of oxalic acid is low, a product with extremely excellent gloss can be obtained when the aqueous chromium chloride solution of the present invention is used for metal surface treatment. In the technique described in Patent Document 2 described above, it exists in an aqueous solution due to the use of an organic reducing agent having a large number of carbon atoms such as starch and glucose in order to reduce hexavalent chromium. The amount of oxalic acid is higher than that of the present invention.

  The amount of oxalic acid in the aqueous chromium chloride solution of the present invention is a low level of 8% by weight or less, preferably 6% by weight or less, more preferably 4% by weight or less, more preferably substantially free of chromium. Is. The amount of oxalic acid can be measured, for example, by ion chromatography. Although there is no restriction | limiting in particular in the lower limit of content of the oxalic acid in the chromium chloride aqueous solution of this invention, If it uses the manufacturing method mentioned later, it can be made into the very low level which does not contain oxalic acid substantially.

  The aqueous chromium chloride solution of the present invention is also characterized by a low level of total organic carbon (hereinafter also referred to as TOC). As a result of the examination by the present inventors, in addition to the low content of oxalic acid described above, when the TOC is low, the aqueous chromium chloride solution of the present invention is used as a metal surface treatment agent. It has been found that a product with even better gloss can be obtained.

  TOC is the total amount of C remaining in the solution as an organic substance. The aqueous chromium chloride solution of the present invention has a low TOC level of preferably 4% by weight or less, preferably 2% by weight or less, based on chromium. In Patent Document 2 described above, it is described that 0.3% by weight or more of TOC is required in a chromium nitrate aqueous solution in order to reliably reduce hexavalent chromium to trivalent chromium. However, when the present inventors examined the TOC in detail, it was found that when the amount of TOC was increased, sufficient gloss could not be obtained when an aqueous chromium chloride solution was used as a metal surface treatment agent. If the chromium chloride aqueous solution of the present invention is produced by the production method described later, even if the TOC is at a low level, hexavalent chromium can be surely eliminated. Although there is no restriction | limiting in particular in the lower limit of TOC in the chromium chloride aqueous solution of this invention, If it uses the manufacturing method mentioned later, it can be made into the very low level of 0.5 weight%.

  The TOC in the chromium chloride aqueous solution of the present invention can be measured by, for example, a TOC500 type total organic carbon meter manufactured by Shimadzu Corporation.

  The aqueous chromium chloride solution of the present invention is substantially free of hexavalent chromium in the aqueous solution, despite the low level of TOC. Therefore, the chromium chloride aqueous solution of the present invention has an advantage that the environmental load is small. Such an aqueous solution is suitably produced by a production method described later.

The aqueous chromium chloride solution of the present invention contains a compound of the composition formula Cr (OH) xCly (where 0 ≦ x ≦ 2, 1 ≦ y ≦ 3, x + y = 3). In many cases, the aqueous chromium chloride solution of the present invention is an aqueous solution of 25% by weight or more, preferably 35% by weight or more in terms of CrCl ₃ . If it exceeds 41% by weight, crystals will precipitate depending on the conditions. In addition to chromium chloride represented by CrCl ₃ , the compound represented by the composition formula includes basic chromium chloride which is a compound in which a part of chlorine is substituted with a hydroxyl group, that is, 0 <x ≦ 2, 1 ≦ y <3, x + y = 3 are included. Examples of basic chromium chloride include Cr (OH) _0.5 Cl _2.5 , Cr (OH) Cl ₂ , Cr (OH) ₂ Cl and the like. In the following description, the term “chromium chloride” may mean chromium chloride represented by CrCl ₃ depending on the context, and may mean basic chromium chloride. In some cases, both are simply called chromium chloride.

  The compounds represented by the above composition formulas may be present alone or in any combination of two or more in the chromium chloride aqueous solution of the present invention. By combining two or more kinds, a solution suitable for a specific application can be prepared.

  When the chromium chloride aqueous solution of the present invention has x = 0 and y = 3 in the above composition formula, the specific gravity at 20 ° C. of the aqueous solution is preferably 1.25 to 1.46.

  On the other hand, when the chromium chloride aqueous solution of the present invention is a basic chromium chloride aqueous solution, the aqueous solution preferably has a specific gravity at 20 ° C. of preferably 1.35 to 1.44, more preferably 1.40 to 1.44. is there. If the specific gravity of the aqueous solution is within this range, the liquid will not be deviated even if stored for a long period of time, and chromium chloride crystals are less likely to precipitate. In order to set the specific gravity within the above range, for example, as described below, the molar ratio (Cl / Cr) of chlorine and chromium in basic chromium chloride may be 1 or more and less than 3.

  In the basic chromium chloride aqueous solution, the molar ratio (Cl / Cr) of chlorine and chromium in the basic chromium chloride is preferably 1 or more and less than 3. If the molar ratio is within this range, chromium chloride crystals are less likely to be generated. In the present invention, the specific gravity and the molar ratio of chlorine and chromium described above are important factors for preventing crystallization of chromium chloride more effectively.

  In order to make the molar ratio of chlorine and chromium in the basic chromium chloride within the above range, for example, a production method described later may be used.

  The concentration of basic chromium chloride in the basic chromium chloride aqueous solution is appropriately adjusted according to the specific application. In general, it is preferably 8.2% by weight or more, particularly 11.4% by weight or more in terms of Cr. The upper limit of the concentration is not particularly limited, but is suitably about 14% by weight, particularly about 13.5%. The concentration of basic chromium chloride can be easily adjusted by adding dilution water such as ion exchange water or pure water. Accordingly, the basic chromium chloride aqueous solution of the present invention has an advantage that the concentration of chromium chloride can be freely adjusted according to the purpose of use.

Since hexavalent chromium compounds have erosion and oxidation properties, a large amount of impurity metal ions, especially Na, Fe and Cu, are inevitably mixed in the chromium chloride aqueous solution obtained from the hexavalent chromium compound. On the other hand, the chromium chloride aqueous solution of the present invention is also characterized by the extremely low content of these ions. Specifically, the impurity metal ions in the aqueous chromium chloride solution are at a low level of preferably not more than 30 ppm, more preferably not more than 20 ppm per 40% by weight as CrCl ₃ . Cu is preferably 30 ppm or less, more preferably 20 ppm or less. Regarding Fe, it is preferably 20 ppm or less, more preferably 10 ppm or less. Such a high-purity chromium chloride aqueous solution is particularly preferable when it is used for the production of chromium hydroxide used as a raw material for a chromium catalyst because an advantageous effect that high-purity chromium hydroxide is obtained can be obtained. For example, ICP-AES is used for measuring the concentration of impurity metal ions.

  The basic chromium chloride aqueous solution of the present invention is also characterized by being substantially free of free chlorine ions not bound to Cr. It is preferable that substantially no free chlorine ions are contained, because, for example, when the aqueous chromium chloride solution of the present invention is stored at a high concentration for a long period of time, it is possible to suppress the precipitation of crystals.

  The aqueous chromium chloride solution of the present invention can be preferably used for, for example, metal surface treatment and catalyst. In particular, when used for metal surface treatment, there is an advantage that a product with excellent gloss can be obtained.

  Next, the suitable manufacturing method of the chromium chloride aqueous solution of this invention is demonstrated. In the production method, as a first step of the reaction, an organic reducing agent is added to the aqueous chromic acid solution to reduce part of the chromic acid in advance, and then hydrochloric acid and the organic reducing agent are mixed and added. , Characterized in that the reaction is completed.

  First, the chromic acid aqueous solution, which is a raw material, is obtained, for example, by dissolving chromium trioxide obtained by performing various purification treatments in water using sodium chromate obtained by alkaline oxidation roasting of chrome ore as a starting material. . The chromic acid aqueous solution thus obtained is a chromic acid aqueous solution prepared by adding chromium hydroxide or chromium carbonate obtained by adding caustic soda or soda ash to chromium sulfate, or high carbon ferrochromium with sulfuric acid or hydrochloric acid. Impurities such as Fe, Na, Mg, Al, Ca, Ni, Mo, and W are extremely small compared to the chromic acid aqueous solution obtained by dissolution.

  The aqueous chromic acid solution may be a solution in the reaction system, and chromium trioxide can be used in the initial reaction. However, in many cases, an aqueous solution prepared by adding and dissolving water is used. Although there is no restriction | limiting in particular in the density | concentration of chromic acid aqueous solution, It is preferable that it is 20 to 60 weight% as a general range.

  The organic reducing agent added to the chromic acid aqueous solution is not particularly limited as long as it is almost decomposed into carbon dioxide gas and water in the reduction reaction described later and substantially no organic decomposition product remains. For example, monohydric alcohols such as methanol and dihydric alcohols such as ethylene glycol and trimethylene glycol are preferably used. As other organic reducing agents, monosaccharides such as glucose, disaccharides such as maltose, and polysaccharides such as starch can be used. However, when a saccharide having a large number of carbon atoms is used, organic decomposition products are likely to remain, and oxalic acid It is not easy to make the content low. Moreover, it is not easy to make TOC containing oxalic acid low. Therefore, in this production method, it is preferable to use a monohydric or dihydric alcohol which is a reducing agent that is less likely to produce oxalic acid and can easily reduce the TOC to a low level. Moreover, when monohydric or dihydric alcohol is used, there also exists an advantage that the reductive reaction near a stoichiometric amount is easy to be obtained. From these viewpoints, it is preferable to use a lower alcohol (for example, an alcohol having 4 or less carbon atoms), particularly methanol, ethylene glycol or trimethylene glycol, and particularly preferably methanol.

  The organic reducing agent may be added in a state diluted with water. When diluting in water, the concentration of the organic reducing agent is preferably about 10 to 30% by weight from the viewpoint of operability and reaction management.

  As hydrochloric acid added to the chromic acid aqueous solution together with the organic reducing agent, industrial ones can be used, and either synthetic hydrochloric acid or by-product hydrochloric acid may be used. Usually, the concentration is 35% by weight and the specific gravity is 1.15. However, it is not limited to this. These raw materials are desirably used at as high a concentration as possible for the purposes of the present invention.

  First, as the first step of the reaction, an organic reducing agent is added to the chromic acid aqueous solution, and after a part of chromic acid is reduced in advance, hydrochloric acid and the organic reducing agent are mixed and added to the chromic acid aqueous solution. There is no restriction | limiting in particular in each addition rate. In the method of mixing an acid and a chromic acid aqueous solution in advance and adding an organic reducing agent as in the method described in Patent Document 2, in the production of chromium chloride, the temperature rises due to the heat of reaction of the oxidation-reduction reaction. It is dangerous because chromyl chloride is generated.

For example, the reaction formula of this production method when methanol is used as the organic reducing agent is as follows (wherein x represents a number of 0 or more and 3 or less).
2H ₂ CrO ₄ + 2xHCl ₃ + CH ₃ OH → 2Cr (OH) _3-x Cl _x + CO ₂ + (2x + 1) H ₂ O

  As shown in the above reaction formula, the theoretical amount (stoichiometric amount) of hydrochloric acid required to convert chromic acid to chromium chloride is a, and the theoretical amount (stoichiometric amount) of the organic reducing agent required to reduce chromic acid. When the theoretical amount is b, it is preferable to always maintain the relationship of a <b while the reducing agent is added. As described above, as a first step of the reaction, an organic reducing agent is added to reduce a part of chromic acid in advance, and then a mixed solution of hydrochloric acid and a reducing agent is added. This addition method does not require a high degree of management, can always maintain the relationship of a <b, and is a preferable method from the viewpoint of operability. Thus, there is an advantageous effect of suppressing generation of chromyl chloride by reacting hydrochloric acid and chromic acid which are not bonded to trivalent chromium.

  Addition of an organic reducing agent to the chromic acid aqueous solution initiates a redox reaction. The reaction proceeds rapidly with a considerable exotherm. The reaction temperature is usually 90 to 110 ° C. The generated water vapor is cooled by a condenser and refluxed into the reaction system.

  In order to obtain a basic chromium chloride aqueous solution, hydrochloric acid may be added in an amount of 1 to 3 molar equivalents relative to chromic acid.

After completion of the reaction, it can be aged for a while and used as it is. The aging is preferably performed at 90 to 110 ° C. for 30 minutes or more. The main purpose of such aging is to make Cr ⁶⁺ present in the solution substantially zero and to make the content of oxalic acid 8% by weight or less with respect to chromium. If necessary, an organic reducing agent is further added to completely reduce the remaining Cr ⁶⁺ . Further, if necessary, hydrochloric acid may be added to finely adjust the molar ratio of chromium ions to chlorine ions.

  The aqueous chromium chloride solution obtained by this production method has a low oxalic acid content and is substantially free of hexavalent chromium. Chromium chloride crystals can be obtained by concentrating the resulting chromium chloride aqueous solution by heating and cooling if necessary. The resulting chromium chloride crystals have a low level of oxalic acid content of 2% by weight or less, preferably substantially free of chromium. Moreover, hexavalent chromium is not substantially contained.

  In the heating concentration, moisture in the chromium chloride aqueous solution may be removed. The concentration by heating may be performed during the reaction even after the reaction is completed. In the case of concentrating by heating during the reaction, it is efficient and industrially advantageous to concentrate by condensing the generated water vapor with a condenser and extracting the water out of the reaction system.

  The present invention will be specifically described below with reference to examples. Unless otherwise specified, “%” means “% by weight”.

[Example 1]
Into a glass reaction vessel with a condenser, 251.6 g of water was added, and 253.1 g of chromium trioxide was added, and the mixture was sufficiently stirred and dissolved to obtain a 50% aqueous chromic acid solution. Methanol was used as the reducing agent. As a first step of the reaction, a 20% aqueous methanol solution in which 48.4 g of water was added to 12.2 g of 99.5% methanol was added to the aqueous chromic acid solution using a metering pump at a rate of 1.0 g / min. This addition rate is a rate at which 60.6 g of a 20% aqueous methanol solution is added in about 1 hour. Further, 12.2 g of 99.5% methanol is an amount corresponding to 30% reduction of chromic acid.

After the addition of the reducing agent in the first stage, 817.9 g of a mixed solution of 28.4 g of 99.5% methanol and 789.5 g of 35% hydrochloric acid was added at a rate of 6.8 g / min. This addition rate is a rate at which 817.9 g of a mixed solution of methanol and hydrochloric acid is added in 2 hours. During the reaction, 327.7 g of condensed water was extracted out of the system and concentrated. After completion of the addition of the mixed solution of reducing agent and hydrochloric acid, ripening was continued for 30 minutes. The temperature at this time was 105 ° C. After aging, the remaining Cr ⁶⁺ was checked, and methanol solution was added to continue aging. The reaction was terminated after confirming that the color development of Cr ⁶⁺ disappeared by the diphenylcarbagit method described below. No generation of chromyl chloride was observed during the reaction. The composition of the obtained chromium chloride aqueous solution was as follows.

<Detection method of hexavalent chromium by diphenylcarbagit method>
A small amount of the reaction solution was placed in a watch glass, and 3 to 5 drops of (1 + 5) sulfuric acid was added dropwise. Diphenylcarbagit was added dropwise thereto, and the point at which the color did not change to red purple was taken as the end point of the reduction reaction.

[Example 2]
A glass reaction vessel with a condenser was charged with 420.6 g of a 60% aqueous chromic acid solution and 84.1 g of water, and sufficiently stirred to obtain a 50% aqueous chromic acid solution. Ethylene glycol was used as the reducing agent. As the first step of the reaction, 20% ethylene glycol aqueous solution in which 56.2 g of water was added to 14.3 g of 98.5% ethylene glycol was added to the chromic acid aqueous solution using a metering pump at a rate of 1.2 g / min. . This addition rate is a rate at which 70.5 g of a 20% ethylene glycol aqueous solution is added in about 1 hour. In addition, 14.3 g of 98.5% ethylene glycol is an amount corresponding to 30% reduction of chromic acid.

After the addition of the reducing agent in the first stage, 822.9 g of a mixed solution of 93.4% ethylene glycol 33.4 g and 35% hydrochloric acid 789.5 g was added at a rate of 6.9 g / min. This addition rate is a rate at which 822.9 g of a mixed solution of ethylene glycol and hydrochloric acid is added in 2 hours. During the reaction, 331.5 g of condensed water was extracted out of the system and concentrated. After completion of the addition of the mixed solution of reducing agent and hydrochloric acid, ripening was continued for 30 minutes. The temperature at this time was 105 ° C. After aging, the remaining Cr ⁶⁺ was checked, and further aging was continued by adding an ethylene glycol aqueous solution. The reaction was terminated after confirming that the color development of Cr ⁶⁺ was lost by the diphenylcarbazite method. No generation of chromyl chloride was observed during the reaction. The composition of the obtained chromium chloride aqueous solution was as follows.

Example 3
A glass reaction vessel with a condenser was charged with 420.6 g of 60% liquid chromic acid and 151.1 g of water, and sufficiently stirred to obtain a 44% chromic acid aqueous solution. 99.5% methanol was used as the reducing agent. As a first step of the reaction, a 20% aqueous methanol solution in which 48.4 g of water was added to 12.2 g of 99.5% methanol was added to the aqueous chromic acid solution using a metering pump at a rate of 1.0 g / min. This addition rate is a rate at which 60.6 g of a 20% aqueous methanol solution is added in about 1 hour. Further, 12.2 g of 99.5% methanol is an amount corresponding to 30% reduction of chromic acid.

After the addition of the reducing agent in the first stage, 423.2 g of a mixed solution of 28.4 g of 99.5% methanol and 394.8 g of 35% hydrochloric acid was added at a rate of 3.5 g / min. This addition rate is a rate at which 423.2 g of a mixed solution of methanol and hydrochloric acid is added in 2 hours. After completion of the addition of the mixed solution of reducing agent and hydrochloric acid, ripening was continued for 30 minutes. The temperature at this time was 105 ° C. After aging, the remaining Cr ⁶⁺ was checked, and methanol solution was added to continue aging. The reaction was terminated after confirming that the color development of Cr ⁶⁺ was lost by the diphenylcarbazite method. No generation of chromyl chloride was observed during the reaction. The composition of the obtained chromium chloride aqueous solution was as follows.

Example 4
256.0 g of water was put into a glass reaction vessel with a condenser, and further 256.0 g of chromium trioxide was added and dissolved with sufficient stirring to obtain a 50% aqueous chromic acid solution. As the reducing agent, 98.5% ethylene glycol was used. As a first step of the reaction, 27% ethylene glycol aqueous solution in which 38.9 g of water was added to 15.0 g of 98.5% ethylene glycol was added to the chromic acid aqueous solution using a metering pump at a rate of 0.9 g / min. . This addition rate is a rate at which 53.9 g of a 27% ethylene glycol aqueous solution is added in about 1 hour. Further, 15.0 g of 98.5% ethylene glycol is an amount corresponding to 31% reduction of chromic acid.

After the addition of the reducing agent in the first stage, 433.0 g of a mixed solution of 98.5% ethylene glycol 33.3 g and 35% hydrochloric acid 399.7 g was added at a rate of 3.6 g / min. This addition rate is a rate at which 433.0 g of a mixed solution of ethylene glycol and hydrochloric acid is added in 2 hours. After completion of the addition of the mixed solution of reducing agent and hydrochloric acid, ripening was continued for 30 minutes. The temperature at this time was 105 ° C. After aging, the remaining Cr ⁶⁺ was checked, and further aging was continued by adding an ethylene glycol aqueous solution. The reaction was terminated after confirming that the color development of Cr ⁶⁺ was lost by the diphenylcarbazite method. No generation of chromyl chloride was observed during the reaction. The composition of the obtained chromium chloride aqueous solution was as follows.

Example 5
A glass reaction vessel with a condenser was charged with 420.6 g of 60% liquid chromic acid and 84.1 g of water, and sufficiently stirred to obtain a 50% chromic acid aqueous solution. 99.5% methanol was used as the reducing agent. As a first step of the reaction, a 20% aqueous methanol solution in which 48.4 g of water was added to 12.2 g of 99.5% methanol was added to the aqueous chromic acid solution using a metering pump at a rate of 1.0 g / min. This addition rate is a rate at which 60.6 g of a 20% aqueous methanol solution is added in about 1 hour. Further, 12.2 g of 99.5% methanol is an amount corresponding to 30% reduction of chromic acid.

After completing the addition of the reducing agent in the first stage, 554.8 g of a mixed solution of 28.4 g of 99.5% methanol and 526.4 g of 35% hydrochloric acid was added at a rate of 4.6 g / min. This addition rate is a rate at which 554.8 g of a mixed solution of methanol and hydrochloric acid is added in 2 hours. During the reaction, 64.6 g of condensed water was extracted out of the system and concentrated. After completion of the addition of the mixed solution of reducing agent and hydrochloric acid, ripening was continued for 30 minutes. The temperature at this time was 105 ° C. After aging, the remaining Cr ⁶⁺ was checked, and methanol solution was added to continue aging. The reaction was terminated after confirming that the color development of Cr ⁶⁺ was lost by the diphenylcarbazite method. No generation of chromyl chloride was observed during the reaction. The composition of the obtained chromium chloride aqueous solution was as follows.

Example 6
A glass reaction vessel with a condenser was charged with 420.6 g of 60% liquid chromic acid and 84.1 g of water, and sufficiently stirred to obtain a 50% chromic acid aqueous solution. 99.5% methanol was used as the reducing agent. As a first step of the reaction, a 20% aqueous methanol solution in which 48.4 g of water was added to 12.2 g of 99.5% methanol was added to the aqueous chromic acid solution using a metering pump at a rate of 1.0 g / min. This addition rate is a rate at which 60.6 g of a 20% aqueous methanol solution is added in about 1 hour. Further, 12.2 g of 99.5% methanol is an amount corresponding to 30% reduction of chromic acid.

After the addition of the reducing agent in the first stage, 686.4 g of a mixed solution of 98.4% methanol 28.4 g and 35% hydrochloric acid 658.0 g was added at a rate of 5.7 g / min. This addition rate is a rate at which 686.4 g of a mixed solution of methanol and hydrochloric acid is added in 2 hours. During the reaction, 196.2 g of condensed water was extracted out of the system and concentrated. After completion of the addition of the mixed solution of reducing agent and hydrochloric acid, ripening was continued for 30 minutes. The temperature at this time was 105 ° C. After aging, the remaining Cr ⁶⁺ was checked, and further aging was continued by adding an ethylene glycol aqueous solution. The reaction was terminated after confirming that the color development of Cr ⁶⁺ was lost by the diphenylcarbazite method. No generation of chromyl chloride was observed during the reaction. The composition of the obtained chromium chloride aqueous solution was as follows.

Example 7
A glass reaction vessel with a condenser was charged with 105.2 kg of a 60% chromic acid aqueous solution and 21.0 kg of water, and stirred sufficiently to obtain a 50% chromic acid aqueous solution. Methanol was used as the reducing agent. As the first stage of the reaction, 20% aqueous methanol solution obtained by adding 12.0 kg of water to 3.0 kg of 99.5% methanol was added to the aqueous chromic acid solution at a rate of 0.25 kg / min using a metering pump. This addition rate is a rate at which 15.0 kg of 20% aqueous methanol solution is added in about 1 hour. Further, 3.0 kg of 99.5% methanol is an amount corresponding to 30% reduction of chromic acid.

After the addition of the reducing agent in the first stage, 204.5 kg of a mixed solution of 99.5% methanol 7.1 kg and 35% hydrochloric acid 197.4 kg was added at a rate of 1.70 kg / min. This addition rate is a rate at which 204.5 kg of a mixed solution of methanol and hydrochloric acid is added in 2 hours. During the reaction, 114.4 kg of condensed water was extracted out of the system and concentrated. After completion of the addition of the mixed solution of reducing agent and hydrochloric acid, ripening was continued for 30 minutes. The temperature at this time was 105 ° C. After aging, the remaining Cr ⁶⁺ was checked, and further aging was continued by adding an ethylene glycol aqueous solution. The reaction was terminated after confirming that the color development of Cr ⁶⁺ was lost by the diphenylcarbazite method. No generation of chromyl chloride was observed during the reaction. After completion of the reaction, the reaction mixture was cooled to room temperature and stirring was continued for a whole day and night. The precipitated crystals were separated by a centrifugal separator, and 61 kg of chromium chloride crystals were recovered. The obtained crystal was confirmed to be CrCl ₃ .6H ₂ O by X-ray diffraction. The composition of the obtained chromium chloride crystals was as follows.

[Comparative Example 1]
Into a glass reaction vessel with a condenser, 251.6 g of water was added, and 253.1 g of chromium trioxide was added, and the mixture was sufficiently stirred and dissolved to obtain a 50% aqueous chromic acid solution. Glucose was used as the reducing agent. As the first stage of the reaction, a 20% glucose aqueous solution in which 67.6 g of water was added to 17.6 g of 97% glucose was added to the aqueous chromic acid solution at a rate of 1.4 g / min using a metering pump. This addition rate is a rate at which 85.2 g of a 20% glucose aqueous solution is added in about 1 hour. Moreover, 17.6 g of 97% glucose is an amount corresponding to 30% reduction of chromic acid.

After the addition of the reducing agent in the first stage, 830.5 g of a mixed solution of 41.0 g of 97% glucose and 789.5 g of 35% hydrochloric acid was added at a rate of 6.9 g / min. This addition rate is a rate at which 830.5 g of a mixed solution of glucose and hydrochloric acid is added in 2 hours. During the reaction, 337.0 g of condensed water was extracted out of the system and concentrated. After completion of the addition of the mixed solution of reducing agent and hydrochloric acid, ripening was continued for 30 minutes. The temperature at this time was 105 ° C. After aging, the remaining Cr ⁶⁺ was checked, and an aqueous glucose solution was added to continue aging. The reaction was terminated after confirming that the color development of Cr ⁶⁺ was lost by the diphenylcarbazite method. No generation of chromyl chloride was observed during the reaction. The composition of the obtained chromium chloride aqueous solution was as follows.

[Performance evaluation]
The chromate treatment solution was erected using the aqueous chromium chloride solution obtained in Examples 1 to 6 and Comparative Example 1, and the test piece of the galvanized steel sheet was immersed and dried for chromate treatment. The degree of gloss after the treatment was evaluated. The results are shown in Table 9 below. In the table, ◎ indicates that the gloss is very good, ○ indicates that the gloss is good, and x indicates that the gloss is not sufficient.

  As is clear from the above results, it can be seen that when the chromium chloride aqueous solution of the example (product of the present invention) is used, the gloss by the chromate treatment is excellent.

  Furthermore, the ease of crystallization of the aqueous chromium chloride solutions obtained in Examples 4 and 5 and Comparative Example 1 was evaluated. About 40 ml of each sample was placed in a 50 ml plastic container, covered, and allowed to stand in an environment of room temperature and minus 0 degrees or less, and then the presence or absence of crystals was visually observed. The presence or absence of a crystal was determined as a crystal because even a fine crystal may grow as a nucleus. The results are shown in Table 10.

As shown in Table 10, it can be seen that in the solutions obtained in Examples 4 and 5, no crystals are observed even when stored at minus 0 degrees or less. On the other hand, crystals were observed when the solution obtained in Comparative Example 1 which is a typical example of the liquid composition of the conventional chromium chloride aqueous solution was stored near 0 degree.

Claims (12)

  A chromium chloride aqueous solution, wherein the content of oxalic acid is 8% by weight or less based on chromium.   The aqueous chromium chloride solution according to claim 1, wherein the total organic carbon is 4% by weight or less based on chromium.   The aqueous chromium chloride solution according to claim 1 or 2, comprising basic chromium chloride represented by a composition formula Cr (OH) xCly (where 0 <x≤2, 1≤y <3, x + y = 3).   The aqueous chromium chloride solution according to claim 3, wherein the specific gravity at 20 ° C is 1.35 to 1.44, and the molar ratio of chlorine to chromium (Cl / Cr) is 1 or more and less than 3.   The aqueous chromium chloride solution according to claim 3 or 4, wherein the concentration is 8.2 to 14% by weight in terms of Cr. 6. The aqueous chromium chloride solution according to claim 1, wherein the impurity metal ions in the aqueous solution are Na ≦ 30 ppm and Fe ≦ 20 ppm per 40% by weight as CrCl ₃ .   The aqueous chromium chloride solution according to any one of claims 3 to 5, which is substantially free of free chlorine ions not bonded to Cr.   As a first step of the reaction, an organic reducing agent comprising a monohydric alcohol or a dihydric alcohol is added to the aqueous chromic acid solution to reduce part of the chromic acid in advance, and then hydrochloric acid and the organic reducing agent are added. A method for producing a chromium chloride aqueous solution, which is added by mixing to complete the reaction.   The method for producing a chromium chloride aqueous solution according to claim 8, wherein the monohydric alcohol or dihydric alcohol is methanol, ethylene glycol or trimethylene glycol.   The method for producing a chromium chloride aqueous solution according to claim 8 or 9, wherein hydrochloric acid is added in an amount of 1 to 3 molar equivalents relative to chromic acid.   A chromium chloride crystal characterized by having an oxalic acid content of 2% by weight or less based on chromium. As a first step of the reaction, an organic reducing agent comprising a monohydric alcohol or a dihydric alcohol is added to the aqueous chromic acid solution to reduce part of the chromic acid in advance, and then hydrochloric acid and the organic reducing agent are added. A method for producing a chromium chloride crystal, comprising mixing and adding to complete a reaction to obtain a chromium chloride aqueous solution, followed by heating and concentrating the chromium chloride aqueous solution and further cooling to precipitate a chromium chloride crystal.